title: Autoimmune, neurological, and venous thromboembolic adverse events after immunisation of adolescent girls with quadrivalent human papillomavirus vaccine in Denmark and Sweden: cohort study.
abstract: OBJECTIVE
  To assess the risk of serious adverse events after vaccination of adolescent girls with quadrivalent human papillomavirus (qHPV) vaccine.
  
  
  METHODS
  Register based cohort study.
  
  
  METHODS
  Denmark and Sweden, October 2006 to December 2010.
  
  
  METHODS
  997,585 girls aged 10-17, among whom 296,826 received a total of 696,420 qHPV vaccine doses.
  
  
  METHODS
  Incident hospital diagnosed autoimmune, neurological, and venous thromboembolic events (53 different outcomes) up to 180 days after each qHPV vaccine dose. Only events with at least five vaccine exposed cases were considered for further assessment. Rate ratios adjusted for age, country, calendar year, and parental country of birth, education, and socioeconomic status were estimated, comparing vaccinated and unvaccinated person time. For outcomes where the rate ratio was significantly increased, we regarded three criteria as signal strengthening: analysis based on 20 or more vaccine exposed cases (reliability), rate ratio 3.0 or more (strength), and significantly increased rate ratio in country specific analyses (consistency). We additionally assessed clustering of events in time and estimated rate ratios for a risk period that started on day 181.
  
  
  RESULTS
  Among the 53 outcomes, at least five vaccine exposed cases occurred in 29 and these were analysed further. Whereas the rate ratios for 20 of 23 autoimmune events were not significantly increased, exposure to qHPV vaccine was significantly associated with Behcet's syndrome, Raynaud's disease, and type 1 diabetes. Each of these three outcomes fulfilled only one of three predefined signal strengthening criteria. Furthermore, the pattern of distribution in time after vaccination was random for all three and the rate ratios for these outcomes in the period from day 181 after vaccination were similar to the rate ratios in the primary risk period. The rate ratios for five neurological events were not significantly increased and there were inverse associations with epilepsy (rate ratio 0.66, 95% confidence interval 0.54 to 0.80) and paralysis (0.56, 0.35 to 0.90). There was no association between exposure to qHPV vaccine and venous thromboembolism (0.86, 0.55 to 1.36).
  
  
  CONCLUSIONS
  This large cohort study found no evidence supporting associations between exposure to qHPV vaccine and autoimmune, neurological, and venous thromboembolic adverse events. Although associations for three autoimmune events were initially observed, on further assessment these were weak and not temporally related to vaccine exposure. Furthermore, the findings need to be interpreted considering the multiple outcomes assessed.
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm 171 77, Sweden.
authors.forename: Lisen
authors.initials: L
authors.lastname: Arnheim-Dahlström
authors.forename: Björn
authors.initials: B
authors.lastname: Pasternak
authors.forename: Henrik
authors.initials: H
authors.lastname: Svanström
authors.forename: Pär
authors.initials: P
authors.lastname: Sparén
authors.forename: Anders
authors.initials: A
authors.lastname: Hviid
mesh_terms: D000293:Adolescent; D001327:Autoimmune Diseases / Q000453:epidemiology* / Q000276:immunology; D002648:Child; D015331:Cohort Studies; D003718:Denmark / Q000453:epidemiology; D005260:Female; D006801:Humans; D015994:Incidence; D009422:Nervous System Diseases / Q000453:epidemiology* / Q000276:immunology; D030361:Papillomavirus Infections / Q000517:prevention & control*; D053918:Papillomavirus Vaccines / Q000009:adverse effects*; D012307:Risk Factors; D013548:Sweden / Q000453:epidemiology; D054556:Venous Thromboembolism / Q000453:epidemiology* / Q000276:immunology
chemical_list: D053918:Papillomavirus Vaccines